fix(tools): cancel rejected image download streams

[xiaofeilovecoding]

What does this PR do, and why?

Cancel image-download response bodies before reporting HTTP errors or unsupported content types. Preserve the original error if cancellation fails.

Linked issue

Fixes #984.

How did you verify it?

Windows, Bun 1.3.14:

• Five regressions pass using the real tool, local HTTP and a Node HTTP-to-Web stream bridge.
• Backend typecheck, changed-file formatting and gitleaks pass.
• Broader tests hit existing Windows path/symlink failures; the path failure also reproduces on unchanged main.
• Full bun run check and monorepo typecheck are blocked by an unchanged tracked symlink checked out as text. Later full-check stages have not run; full verification still needs Linux CI.

Checklist

• bun run check is green (Windows limitation above)
• CHANGELOG.md has an Unreleased entry
• No version bumps

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